LTE (Long Term Evolution) system adopts HARQ (Hybrid Automatic Repeat request) to improve the reliability of the data transmission. After turning on the downlink HARQ function, UE (User Equipment) decodes the received downlink assignment, if the decoding is correct, UE feeds back ACK to the base station, if the decoding failure, UE feeds back NACK to the base station and requires the base station to transmit the assignment again. When the semi-persistent downlink scheduling service is finished, the base station will send the SPS (Semi-persistent Scheduling) resource release indication to UE, and notify the UE to release all resources which configured for the service. UE will feed back ACK to base station after the UE correctly received the indication.
For the LTE multi-carrier aggregation system, the base station uses more than one downlink carrier in a sub-frame to send the data to UE, each carrier has an independent HARQ entity, therefore, UE needs to feed back multiple ACK/NACK information in a uplink sub-frame.
For the above-mentioned ACK/NACK feedback problems, existing technology defined in LTE Rel-8 can be used for feedback transmission, specific comprising: bundling and multiplexing, namely, using one PUCCH (Physical Uplink Control Channel) channel resource to feed back multiple ACK/NACK information. These two methods are described in the following respectively, therein, assuming that the feedback window length is L, L is the number of downlink sub-frames which need to feed back the ACK/NACK information in the same uplink sub-frame. For FDD system, L equal to 1; and for TDD system, L equal to M. For different uplink-downlink configuration and uplink sub-frame, the value of M is different, it is shown in table 1, the number of K in each row.
TABLE 1Downlink assoviation set index K: {k0, k1, • • • kM−1} for TDDUL-DLConfig-Subframe nuration01234567890——6—4——6—41——7, 64———7, 64—2——8, 7, 4, 6————8, 7,——4, 63——7, 6, 116, 55, 4—————4——12, 8, 7, 116, 5,——————4, 75——13, 12, 9, 8,———————7, 5, 4, 11, 66——775——77—
For ACK/NACK bundling mode, performing logic AND for M′ ACK/NACK corresponding to the same user and same codeword, getting 1 or 2 bit (downlink two codewords) feedback information, FIG. 1 shows that single codeword and multiple codeword bundling process. In this case, it just needs to use PUCCH Format 1a/1b to feed back 1 or 2 bit ACK/NACK. The method also can effectively solve the PUCCH coverage problem, and is fitting for the cell edge UE.
For ACK/NACK multiplexing mode, it also applies to the PDSCH with single codeword and multiple codeword. For multiple codeword PDSCH transmission, first of all, performing logic AND for M′ ACK/NACK corresponding to the same user and same codeword; then, according to the state composed by L bundled ACK/NACKs, 2-bit feedback information and channel index for actual transmission are determined by looking up the table, and using PUCCH Format 1b to transmit the 2-bit feedback information in the chose feedback channel. For single codeword PDSCH transmission, the feedback information and feedback channel for actual transmission are directly chosen according to L ACK/NACKs feedback state. It is shown as FIG. 2, actual feedback information is defined for 2 bits, therefore QPSK (Quadrature Phase-Shift Keying) modulation and PUCCH Format 1b transmission are needed. The method avoids unnecessary retransmission effectively, fitting for the cell center user, and improving transmission efficiency.
Whether the bundling or the multiplexing method, UE simply uses one PUCCH channel resource to send an ACK/NACK feedback information, and uplink single-carrier characteristic is maintained.
For dynamic scheduling downlink assignment, the usable uplink channel index for ACK/NACK feedback information is determined by the first CCE (Control Channel Element) index of the PDCCH (Physical Downlink Control Channel) used for transmitting the scheduling information corresponding to the assignment, namely, one uplink feedback channel resource index is uniquely determined according to the first CCE of the PDCCH. For bundling mode, supposing M′ is the number of actually received downlink assignment, uplink control channel resource for actual transmission is indicated by the first CCE of the M′ PDCCH in feedback window; for multiplexing mode, each PDCCH corresponding to a usable uplink channel resource index in the feedback window, and a channel resource for actual transmission is chose from all usable channels according to specific feedback state.
For the ACK/NACK feedback corresponding to downlink semi-persistent scheduling assignment, base station knows specific transmission time location for each information beforehand because they are periodically fed back, therefore, the channels used to transmit above control signal are beforehand configured to UE by base station through RRC signal (Radio Resource Control).
LTE-A system supports up to five carriers for aggregation right now. For carrier aggregation system, feedback window defines the multiple downlink carriers and downlink sub-frames which need to feedback ACK/NACK in the same sub-frame. For FDD system, the size of feedback window L equal to the number of UE aggregated downlink carriers. For TDD system, the size of feedback window L=N×M, therein, N is the number of UE aggregated downlink carriers, M is number of K in each row of table 1.
At present, in LTE-A (LTE-Advanced) system, for UE which configuring multiple transmission antennas, it can use ORTD (Orthogonal Resource Transmit Diversity) for uplink control channel to realize transmit diversity, and improving reliability or capacity of uplink control signaling transmission. The so-called ORTD is each antenna port corresponding to a PUCCH resource index, the same information is spread with the orthogonal sequences corresponding to the different antenna port, and is sent through corresponding antenna ports synchronously. Receiver side separates signal from different antenna ports and performs combination and detection, thereby, and gets diversity gain. FIG. 3 is a flow diagram which uses ORTD for transmit diversity through two antenna ports, therein, s is ACK/NACK feedback information, n1PUCCH and n2PUCCH denote the two different uplink control channel resource indexes for two antenna ports respectively, corresponding to different orthogonal spread sequence.
There are at least the following problems in the existing technology: in Long Term Evolution system, UE may use transmit diversity to transmit ACK/NACK information under multiplexing and bundling mode, it is need to use multiple uplink control resource indexes, there is no specific realization for the method of uplink control channel resource reservation and indication of uplink control resource index now.